On 20.10.2021 00:38, Sean Christopherson wrote:
On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:From: "Maciej S. Szmigiero" <maciej.szmigiero@xxxxxxxxxx> This allows us to return a proper error code in case we spot an underflow. Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++-------------------- 1 file changed, 28 insertions(+), 21 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 97d86223427d..0fffb8414009 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11511,9 +11511,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, const struct kvm_userspace_memory_region *mem, enum kvm_mr_change change) { - if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) - return kvm_alloc_memslot_metadata(kvm, new, - mem->memory_size >> PAGE_SHIFT); + if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) { + int ret; + + ret = kvm_alloc_memslot_metadata(kvm, new, + mem->memory_size >> PAGE_SHIFT); + if (ret) + return ret; + + if (change == KVM_MR_CREATE) + kvm->arch.n_memslots_pages += new->npages; + } else if (change == KVM_MR_DELETE) { + if (WARN_ON(kvm->arch.n_memslots_pages < old->npages)) + return -EIO;This is not worth the churn. In a way, it's worse because userspace can spam the living snot out of the kernel log by retrying the ioctl(). Since underflow can happen if and only if there's a KVM bug, and a pretty bad one at that, just make the original WARN_ON a KVM_BUG_ON. That will kill the VM and also provide the WARN_ON_ONCE behavior that we probably want.
Will do. Thanks, Maciej
